I have 99 Lexus RX300 with 175k miles. Last few months, sometimes when I drive the car, I get a very loud grinding sound coming from behind the glove box. Then, I notice on my screen that the air direction arrows move on their own. Every time this happens, the HVAC system is off, so it happens on it’s own and randomly. The loud noise lasts for about 15 seconds then stops. What could this be?
Also, I should mention the the HVAC system blows fine, but the AC doesn’t blow cold air. I am also able to change the air direction mode manually. I was told by 2 different mechanics that I need Evaporator replaced. Could I also need the “air mix servo” motor replaced?
Air mix servo could be another word for blend door actuator so sure that could be the issue... the actuator gets stuck trying to open or close the door and makes that clicking noise...
@cjbman
What could explain why it comes on randomly without the HVAC system being on?
I think some of them have automatic crap in them that controls the pressure of the air inside your car while your driving. 9 out of 10 times that knocking behind the dash is the blend door though. It could have even come loose from the end of the actuator and just flaps around when there is more pressure coming into the cabin.
A few Ford trucks suffer from the same exact problem. I have heard Ford Everests click behind the dash after the car is shut off too.
